diff --git a/client/errors.go b/client/errors.go
index e5a8a865f9..6878144c41 100644
--- a/client/errors.go
+++ b/client/errors.go
@@ -58,31 +58,6 @@ func (e objectNotFoundError) Error() string {
 	return fmt.Sprintf("Error: No such %s: %s", e.object, e.id)
 }
 
-// IsErrUnauthorized returns true if the error is caused
-// when a remote registry authentication fails
-//
-// Deprecated: use errdefs.IsUnauthorized
-func IsErrUnauthorized(err error) bool {
-	return errdefs.IsUnauthorized(err)
-}
-
-type pluginPermissionDenied struct {
-	name string
-}
-
-func (e pluginPermissionDenied) Error() string {
-	return "Permission denied while installing plugin " + e.name
-}
-
-// IsErrNotImplemented returns true if the error is a NotImplemented error.
-// This is returned by the API when a requested feature has not been
-// implemented.
-//
-// Deprecated: use errdefs.IsNotImplemented
-func IsErrNotImplemented(err error) bool {
-	return errdefs.IsNotImplemented(err)
-}
-
 // NewVersionError returns an error if the APIVersion required
 // if less than the current supported version
 func (cli *Client) NewVersionError(APIrequired, feature string) error {
diff --git a/client/plugin_install.go b/client/plugin_install.go
index c8284c5d87..3a740ec4f6 100644
--- a/client/plugin_install.go
+++ b/client/plugin_install.go
@@ -107,7 +107,7 @@ func (cli *Client) checkPluginPermissions(ctx context.Context, query url.Values,
 			return nil, err
 		}
 		if !accept {
-			return nil, pluginPermissionDenied{options.RemoteRef}
+			return nil, errors.Errorf("permission denied while installing plugin %s", options.RemoteRef)
 		}
 	}
 	return privileges, nil